The development and implementation of a late blight fungicide spray model for Canadian potato growers

Project Code PRR06-360

Project Lead

Ron Pitblado - University of Guelph

Objective

To establish a weather-based decision model to assist growers in determining when fungicides should be applied in an efficient, cost effective and environmentally friendly manner for the control of late blight in potatoes

Summary of Results

Late blight disease can be devastating in weather conditions favourable to the disease, causing losses to crop both in the field and in storage. Growers reduce their production risks by spraying with a series of "protectant" fungicides. The potential cost of failing to control potato foliar diseases, especially late blight, is so high that growers are currently not prepared to risk their crops to a reduced spray program. The objective of this project was to establish a new weather-based decision model that could be used across Canada to assist growers in determining when fungicides should be applied for the control of late blight in potatoes.

Initially, four different weather-based decision spray models that have previously been used were compared and evaluated in regions across Saskatchewan, Manitoba, and Ontario. Analysis indicated that these models did not completely address the needs of potato growers, or the delivery was not very grower friendly. In the 2006 season, the number of predicted application dates varied among models even under the same weather conditions per site. As a result of these inconsistencies between current models, a new model called SPUDcast was developed by Weather Innovations Incorporated (WIN) that incorporated the benefits of previous models and added further features to improve acceptance by growers.

SPUDcast can use a leaf wetness sensor (WIN cylindrical LW) rather than just relying on relative humidity measurements. The model incorporates a 3-day forecast to further assist growers in anticipating their spray application decisions. It has two models to address the needs of both smaller and larger potato enterprises.

Model A (timed interval spraying) determines the length of time between initial and subsequent spraying based on a critical threshold value. With 3-day forecasting, model A can anticipate several days ahead when to get ready and spray the potatoes. Model A is proposed to be used in regions where late blight continues to be a threat, yet does not occur every year.

Model B (dynamic dosage model) is used for a 7-day spraying schedule, where growers can choose to alter rates and choice of fungicides. The lowest recommended rate would be used during most of the season, and only when conditions favour disease development would a higher rate of chemical be recommended. Model B is proposed to be used in regions where late blight is a continuing threat, with local outbreaks occurring every year. The 7-10 day schedule is maintained but allows for better decision making when choosing type of fungicide needed and most appropriate label rate to apply. These controlled dosages would decrease the number of systemic or erradicant fungicides used, thereby decreasing financial costs and environmental pesticide loading. SPUDcast was shown to provide recommendations suitable for each region.

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